Production of MRAM devices requires high-temperature processing which in some cases can exceed 200° C. During such processing, it is possible for mobile materials such as manganese (Mn) which is used in an antiferromagnetic layer to diffuse along grain boundaries to a tunnel oxide region. Such diffusion lowers reliability and performance of the MRAM device. Consequently, a method for producing MRAM devices which inhibits the diffusion of mobile materials is desired.